Hey Guys Whats goin on.

My dad is in the process of trying to run two EFI throttle bodies through a dual tunnel ram on a 350 engine. Anyways hes got everything together and were having some issues tunning it properly.

I am trying to convince him that he is going to have to send half the signal to the injectors because he is dumping twice as much fuel and whatnot. We got it running the other day on One carb but it was really ruff. I am not sure exatly what ECU we are using but I beleive its from an 89 305 Z. Also, I have Tunnercat and a programmer so I can modify values.

Have any of you guys ever done or seen a setup like this. If so any details or pics would be great I searched Google and this site and came up with nothing.

Any help would be awesome and if you want any pics let me know its all layed out on the engine stand

Ian

 

go over to the DIY-PROM board, several guys are running, or ahve run setups like this and they can probably help.

 

****, I guess no-one can help me on this??? I though you guys would know for sure

 

You mention "Carb" and "EFI" at the same time...much more info would be needed for assistance (not that I'd be able to give) but...

If in fact you have a twin TB and ECM from an '89 TPI Z, I can see some issues already...

Most likely you're not running twin MAf's...and the ECM you're using would be for a MAF car (165 ECM)

Could it be the TB's you're using are TBI-type setup?

Maybe a pic and better info on the comlete setup would get you some qualified responses.

 

When I say card I mean TBI, and the ECM is from a 305 TBI car with a MAP sensor. Is that possible??? maybe the ECM is wrong, do you know which model ECM I should be running for this type of setup? I will try to get some pics tonight...

Thanks for the replies, keep em comming!!!

Ian

 

how do you have the tbi's wired up? Do you have one of the tbi;'s running off a seperate injector driver or are you trying to run both sets of injectors off of the ecm's internal injector driver? I also take it that your trying to run both sets of injectors at once all the time.

Another thing is that the dual tbi setup is a bit much for a 350. While there is nothing wrong with using the efi, the dual tbi's are going to make fueling at low speeds/loads next to impossible if your trying to do it on a cammed up sbc. The reason being is that the engine has very low volumetric efficiencies at low speeds with a cam and hence it doesnt need anywhere near as much fuel as the two sets of injectors deliver. This is further compounded by the fact that the injectors can only meter fuel down so far before they jsut dont have sufficient time to open up. Id personally run jsut one tbi on a 350.

 

its been done...


i dont have a link to the site, but the jist of it is this:


run them with a straight linkage.. not a progressive one.

you need the IACs in series so that they both open half of what the ECM says

run off only one TPS

i'll go look for the other site...


also look at how GM did the crossfire intake.. crossfire is 2 TBIs on a 305........

 

Here are some pics, let me know what you think

EDIT: Images removed

Ok,
Yes we are trying to run the two at the same time so that there is even flow to all cylinders.

Its a stock engine, nothing crazy. Also, I can take away more fuel by re-programming the eprom. But I will need some help with that.

If you could find something that would be great. Right now we only have one IAC hooked up. But, I think both she be plugged in and just opened half the amount.

I think theres only one TPS but I could be wrong. And, the chip broke a pin so I will have to get another one soon.

 

Hmmmm.... pics need a little work. All I see is 5 banners saying "Thank for stealing our bandwidth... we - todd - did - racing.com

 

If its stock then you definatly dont want to use two at once. Take one off and get a 4 bbl intake and just use a single tbi, youll never get two to function at the same time and have any drivability. If you want more flow, get a 454 bb tbi. They have dual 2 in bores and (most) can be bored out to 2.2 in. if you like.

 

Couldn't you use some of the bit and peices from the Crossfire Injection system? It was a factory dual-TBI system...

 

Try uploading the phots again. Your link is broken.

I'm not sure that wiring two IACs in "series" is going to work, since they are current devices, not voltage devices. Each coil in the stepper motor is phased and alternated either +/- or -/+ to control the direction of the stepping. I'd suggest using just one IAC as a temporary measure, until you can program a PROM with the correct injector constant or injector tables at a given MAP, RPM, amd TPS input.

Teh CFI used a single injector TBI 400 for each throttle body, so the engine still had only two injectors total.

 

Can anyone host for me????

 

Either email your photo to me in an attachment, or compress the image in a JPG format to under 100Kb and attach it to your post.

 

I will attach them instread, sorry for thje mix up.

 

number 2

 

allright

 

As it stands right now we are only using one IAC. Here's an idead that me and my dad were thing could we not put a smaller injector in place of the 305 ones. Like on from a 2.5 L. Or why not use two 2.5 liter throttle bodies in place of the 5.0L. Here's another pic of the stand you can see we have the tranny hooked up aswell. Let me know what you think.

 

The 2.5L injectors wont help much since they flow alot of fuel themselves. The only thing i can suggest for starters is to set the BPW to around 2x what it is now to accomodate the injectors your using and start tuning from there. I think someone on the DIY-PROM board also managed to do away with the IAC throttle follower routine, which would do wonders for your setup since the last thing you want with a good combo is the ecm trying to intervine and try to contol the idle on its own. Youll also want to make sure the IAC counts at idle are as low as possible or zero all together. You can then tune it to make up for the lack of air from the iac. Itll be a bit rich on throttle tip in and so on so youll have to adjust the pump shot and VE tables to account for this. From there it should hopefully be useable enough to get it out on the road so you can do some real tuning. Another thing, what are the exact specs on teh engine? If its a stock smogger or something similar that combo will be the mismatch from hell.

 

Your gonna have to elaborate on some of these terms as I have not done to much tunning work and am not fluent with the abreveations.

Also, I think we will be purchasing a wideband so that we can further tune the motor once in the car.

Thanks for your reply demented. Its people like you that make impossible projects come to life. I will continue to monitor this post of anyone else has any idea's or has found somewhere on the net to get info let me know. The way I look at it is anything is possible if you work at it long enough.

Thanks,
Ian

 

if i remember correctly it stands for base pulse width. The formula for calculating it is:

BPW = [1461.5 x (engine size in Liters / # of cylinders)] / (injector flow rate in gms /sec), with the conversion from pph to gm/sec being # pph *453.6/3600

I think thats right, thats what i have written down, anyway. The injector flow rate would be double in your case (45 or 55 pph x2) so the theoretical value of the BPW would be ~half of what you have now. Did i say double in the above post? I meant half, my mistake. But, the pulse widths will be too short and the fueling will get really funky. Id try moving it down some for starters jsut so you can get it a little leaner. I also found that the stock timing curves where problematic. I couldnt get the engine to idle with them or run properly unless i added in lots of base timing. Of coarse, that really killed WOT performance because all that extra timing meant that i got a good deal of knock counts and the ecm would take the timing out and not fully restore it for several seconds. Theres other stuff youll want to look at as well.

If you dont already have some sort of data logging system, go get it. Winaldl will do ok for starters, there are also DIY real time data logging and software available but winaldl is the easiest to start with. Do a search for the user name JoBy, he has a link in his sig to his home page. There you can download the software. This along with teh WB O2 will definatly help steer you in the right direction. Id definatly go over to the DIY-PROM board and search around. Those guys over there really know their stuff. Alot more so then myself.

 

ok, i jsut got a really wierd idea.... but it might work...


what if you took one injector from each throttle body and ran one of its power wires thru a relay.... now hook the relay to a RPM switch..



so at low RPM, the engine is running off of 2 injectors... the other 2 are bypassed....but when the switch closes you swap back to 4 injectors...

i think the fuel map would look kinda funky at the switch point, but it could be done... right?

 

i had a similar idea when i thought of doing this. The best way to do it, though, would be to use one of the ecms unused outputs to turn on the second set of injectors via an external injector driver and simultaniously halving the BPW so the fueling doesnt have a massive change at the point that the second set of injectors is brought online. IIRC, the aftermarket ecu from holley does somthing similar so their 4 bbl tbi's can be used on smaller HP setups.

 

I am just learning the fuel injection stuff, but maybe I have an idea (I just don't know if it will work)...

You have a tunnel ram on an otherwise stock motor, right? So it would be fairly safe to say that this is mostly for looks? Correct me if my assumption is wrong. If so, couldn't you disable one injector in each throttle body? Then rewire like each active injector is in a single throttle body? It seems to me like only one TPS would need to be hooked up then and the computer would think it is working with a single TBI unit (again, I'm new at this, so maybe I'm way off).

If what I said would work, then you wouldn't be throwing too much fuel at the engine- it'd be like a single unit, but you'd have the look of the dual units. A tunnel ram puts the TBI's far enough away from the heads that there should be plenty of room for a single injector to deliver fuel to each cylinder, even if it is ofset to one side. Anyone think this might work?

 

Just checking back in on this post. Does anyone think what I said before might work?

 

Hmmm... There are some problems in that the airflow delevered from the tbi could possibly exceed the ammount of fuel that would be delevered by one injector. And he'd probably have fuel distribution problems from the fact taht one of the bores would be completly choked with fuel since that injector would have to do double time to keep up with the needed fueling. The easier solution would be to run a pair of hogged out monobodies on it so one ecm w/o any external drivers could be used. This would also make tuning alot easier as well since there arnt 4 injectors taht have to operate together over the entire operating range of the engine.

 

So then would those single throttle bodies be wired up like it was a single unit with duals? In other words, using the wiring from a dual unit, would you just send one injector's wiring to one of the singles and the other injector's wiring to the other? Then just use one TPS?

I always dreamed of a dual TBI unit on a low-rise Edelbrock dual carb manifold, but I don't think I'm smart enough to pull it off.

 

With that setup only having one IAC would be fine since the plenum is so large. On a smaller intake the mixture would be a little (or possibly alot) leaner for the cylinders nearest to the tbi with an IAC when its operational. If you didnt have the throttle follower and used the min air adjustments of the tbis to control the idle it would probably be fine.

 

sorry i could`nt help myself normally i just listen, but ever since i saw the HSR and thought its just a 2x4 bl manifold i wonderd if you could drill a 4 bl manifold for tpi injectors and rails use the tbi for airflow or even a old carb

 

Nothing wrong with that. Its easily doable.

 

My only suggestion is take off those throttle bodies and beat them with a hammer, then get yourself a set of matching carbs. Just my .02 cents.

 

Trooper,
The RPM Air-Gap manifold comes with bosses already built in. There for NO2, but could easly be used for fuel injectors instead of NO2 injectors. I've seen several other manifolds with made in bosses too. That could be a good idea, but there is also a lot of complete set-ups like that already on the market that would take all the guesswork and tuning issues out of the way.

Turbospeed,
Good luck on how ever that motor turns out. It sure is a wild looking set-up thats going to need a lot of tuning. I think that if you can ever get it right it would be able to make some deceant power tghough. I'm building a 388ci now for my '91RS that I plan on using a 700cfm Holley 4bbl TBI unit on. And I thought I was going to have some tuning problems. At least seeing what your tring to tune makes my project seem a lot easier. Good Luck, Bobby

 

With a set of bored out monobodies and a good state of tune he could really have himself quite a setup. With all that plenum volume it could probably feed at least 350 hp before fueling becomes a problem. One of the only real limiting factors will be fuel. Itll be dificult to get over around 220 pph of fuel with only two injectors while still keeping the fuel pressures reasonable.